Dilatation catheters are devices which have an inflatable balloon at the distal end and are utilized in medical procedures such as angioplasty to eliminate stenoses or blockages. The balloons are inserted into vessels in the body to open stenoses or blockages in the vascular system, usually by means of a catheter having a balloon at its distal end. To this end, the catheters may be inserted into a blood vessel, advanced through the blood vessel to a target site (i.e. the location of the stenosis or blockage) and the balloon is then inflated by supplying a liquid such as a radiopaque substance for angiography, through an inflation lumen. The inflation of the balloon causes stretching and expansion of the target site, i.e. a blood vessel, in order to eliminate the stenosis or blockage thereby reestablishing acceptable blood flow.
There are various types of catheters having single or multiple lumen, and some which are over-the-wire and some which are not. For the purpose of the present invention, all catheters will hereinafter be referred to as "balloon catheters."
These devices need a certain degree of lubricity so as to avoid injury to tissues, mucous membranes and other bodily parts with which they come into contact during insertion into a blood vessel, for instance. Balloons are typically made of polymeric materials including nylon, Selar.RTM., polyether-polyester block copolymers (e.g. Hytrel.RTM. or Arnitel.RTM.), poly(amide-ether-ester) block copolymers such as Pebax.RTM., polyethylene terephthalate, polytetrafluoroethylene, polyvinyl chloride, polyurethanes, polyetherurethanes, polyesterurethanes, polyurethane ureas, polyurethane siloxane block copolymers, polyethylene, polypropylene or other similar extrudable thermoplastic, polymeric materials, or composites thereof. Such materials are typically inherently nonlubricious making it necessary to add some type of lubricious coating to the surface in order to advance the device through the blood vessel more easily.
However, once the balloon is at the target site, it will be necessary that it may be retained easily at the site during expansion or contraction without slippage. This is more readily accomplished when the balloon material has no lubricity.
Balloons will therefore typically have a lubricating portion and a non-lubricating portion to avoid what is referred to in the industry as the "watermelon seed" problem wherein a balloon which is too lubricious shoots forward on inflation causing accidental slippage from the target site. U.S. Pat. No. 5,503,631 to Onishi et al. discloses a vasodilating catheter balloon whose body has a lubricating portion and a non-lubricating portion. The lubricious property of the balloon is created by grafting a lubricious coating onto a non-lubricious substrate. Only the tapered portions on opposite ends of the balloon were treated.
The present inventors have now found a simplistic method for coating a balloon prior to formation of the balloon which achieves a lubricious coating gradient necessary for the successful use of a balloon catheter. The balloon exhibits superior retention at the target site without the "watermelon seed" effect, and exhibits excellent lubricity during insertion into the body cavity.